feat: caller context cache invalidation endpoint

- CallerContextService: added invalidateCache(leadId) method
- CallerResolutionController: POST /api/caller/invalidate-context
  endpoint — frontend calls after appointment mutations to bust
  stale AI context cache

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/caller/caller-context.service.ts

@@ -78,6 +78,13 @@ export class CallerContextService {
         return ctx;
     }
 
+    async invalidateCache(leadId: string): Promise<void> {
+        if (!leadId) return;
+        const cacheKey = `${CACHE_KEY_PREFIX}${leadId}`;
+        await this.session.deleteCache(cacheKey).catch(() => {});
+        this.logger.log(`[CALLER-CTX] Cache invalidated for ${leadId}`);
+    }
+
     // Fire-and-forget pre-warm — called from caller resolution
     // so the cache is hot when the AI stream fires seconds later.
     prewarm(leadId: string, patientId: string, auth: string): void {